As a Study Item on LTE-Advanced (Long Term Evolution Advanced) by 3GPP (3rd Generation Partnership Project), standardization of Coordinated multi-point transmission/reception (CoMP) has been examined as one of techniques aiming to increase communication speed of cell-edge mobile station (hereinafter referred to as user equipment (UE)) and improve cell throughput of base stations (hereinafter referred to as eNB: Evolved Node B), for example (see Non Patent Literature 1). An overview of CoMP under examination in LTE-Advanced by 3GPP is explained hereinafter.
In a network introducing CoMP, a scenario for transmitting data to the same UE from multiple transmission points (e.g., eNB or Remote Radio Head (RRH)) at the same timing has been examined as one of CoMP introducing scenarios (Joint Processing (JP)). CoMP using multiple RRHs controlled by the same eNB is referred to as Intra-eNB CoMP, and CoMP among multiple eNBs is referred to as Inter-eNB CoMP. When Joint Processing is performed in Inter-eNB CoMP, it is assumed that one base station controls an UE and remaining base station(s) does not control the UE but transmit data. In this specification, an eNB that controls the target UE is referred to as a Serving eNB, and other eNB not controlling the UE is referred to as a CoMP eNB. The Serving eNB and the CoMP eNB transmit data at the same timing, and the UE receives the data from both eNBs, thereby improving downlink throughput.
FIG. 1 shows a network configuration diagram of a mobile communication system based on a background art as an example. A Serving eNB 901 forms a Serving eNB cell 911, and a CoMP eNB 902 forms a CoMP eNB cell 921. A UE 903 receives data transmitted at the same timing from the Serving eNB cell 911 and the CoMP eNB cell 921. The Serving eNB 901 and the CoMP eNB 902 are each connected to a core network 904 via an access line such as an IP (Internet Protocol) network and relay traffic between the UE 903 and the core network 904. The core network 904 includes a network apparatus (Mobility Management Entity (MME) 905) for controlling the Serving eNB 901 and the CoMP eNB 902, and a Serving Gateway/Packet Data Network Gateway (S/P-GW) 906 for forwarding user data (packet data) to the Serving eNB 901 and the CoMP eNB 902. The MME 905, which is a controlling entity for performing mobility management including UE attach and handover and bearer management, communicates control data with the Serving eNB 901 and the CoMP eNB 902. The S/P-GW 906 is a data transfer entity that transfers user data from/to an external network (PDN: Packet Data Network) to/from the Serving eNB 901 and the CoMP eNB 902.